The proposed research involves two major projects directed toward the goal of finding the biochemical mechanisms underlying differential gene expression and pattern formation in development. The first project is the study of a developmentally regulated Drosophila melanogaster chromosome locus with a known time and tissue of transcription, and a known protein product. The method of study used will be to amplify the locus using recombinant DNA techniques, and to use biochemical procedures to determine some features of its nucleotide sequence organization and transcription. The aim of this study is to gain an understanding of how DNA sequence structure subserves the regulation of gene expression in development. The second project involves the development and use of new techniques that will enable the isolation for study of any regions of the Drosophila genome, regardless of whether their products are known, including those loci important in the cell-cell communications fundamental in developmental pattern formation. The general method will be to produce a catalogue of salivary gland polytene chromosome sites hybridized by random Drosophila recombinant clones, and to use the catalogued recombinants as starting points for successive isolation of overlapping clones, eventually arriving at any location in the Drosophila chromosomes.